Mechanical counterbalance system



J- P. E. KOOI Feb. 27, 1968 MECHANICAL COUNTERBALANCE SYSTEM Filed Oct. 25, 1966 INVENTOR. E E. Koo

PATENT AGENTS United States Patent Ofiice 3,370,556 Patented Feb. 27, 1968 3,379,556 MECHANICAL COUNTERBALANCE SYSTEM Johan Peter Engel Kooi, Ancaster, Ontario, Canada, as-

siguor to Keutfel & Esser of Canada Limited, Montreal, Quebec, Canada Filed Oct. 25, 1966, Ser. No. 589,445 6 Claims. (Cl. 108136) ABSTRAUI OF THE DISCLOSURE A counterbalance system for a drafting table in which the table top is mounted for vertical movement relative to a supporting frame which includes an arm pivoted in the frame and operativelyconnected to the table top with spring means to urge the arm in table elevating direction and such spring means are connected to the frame and to a carriage slidably mounted on the arm and connected by a link to the frame so that movement of the table top and of the arm changes the position of the carriage and compensates the variation in the force of the spring as the table top moves vertically.

The present invention is concerned with improvements in or relating to mechanical counterbalance systems, and especially such systems intended for use as counterbalances for a drafting table.

A particular example of a device requiring a mechanical counterbalance system is a drafting table in which the table top is mounted for vertical movement, so that the operator can quickly and easily adjust its height to suit himself, the counterbalance being operative to reduce the effective weight of the table top.

Simple spring counterbalance arrangements that have been used hitherto usually have the disadvantage that the force supplied by the springs varies widely with the movement of the table top, due to changes in the spring elfort as they change in length.

It is an object of the present invention to provide a new mechanical system providing a compensated force characteristic over a predetermined range of movement of an element thereof.

It is a particular object of the invention to provide a new mechanical counterbalance system having a member with a compensated torque characteristic over a predetermined range of movement thereof.

In accordance with the present invention there is provided a mechanical system comprising a frame, an arm mounted on the frame for movement about a pivot, and means urging the said arm for movement about the pivot over a predetermined range of such movement with a compensated torque characteristic, said urging means comprising a carriage mounted on the arm for radial movement towards and away from the pivot, biasing means connected between the frame and the carriage and urging the carriage and thereby the arm for said movement with a force that changes with the movement, and constraining means operatively connected between the frame and the carriage and constraining the carriage for the said radial movement upon said movement of the arm, such that the change of the radial distance of the carriage from the pivot compensates for the change of the force provided by the biasing means.

A drafting table which embodies a particular preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein:

FIGURE 1 is a general perspective view of the drafting table with parts thereof shown broken away as necessary for the operating mechanism to be seen, and

FIGURES 2 and 3 are cross sections of respective details, taken respectively on the lines 22 and 33 of FIGURE 1.

The drafting table illustrated herein comprises a table body 10 mounted on two spaced elongated parallel feet 11, the body supporting a table top 12 by means of an intervening leg support structure, which comprises two spaced leg assemblies 13. The arrangement is such that the table top can be raised or lowered relative to the body, (as indicated by the arrows 14), and can be tilted at different inclinations relative thereto, (as indicated by the arrows 15).

The table top 12 can be of any conventional construction, and is rigidly secured to two supporting members 16 which are pivotally connected by a pivot pin 17, about a generally horizontal pivot axis, to a respective downwardly-extending leg member 18 of the associated assembly 13. Each member 16 is also pivotally connected by a pin 19 to a subsidiary leg member 2t), the axes of the pins 17 and 19 being parallel to one another, the member 20 being capable of telescoping motion within the associated main leg member 18 to permit the above-described tilting motion of the table top 12.

Each leg assembly 13 is individually mounted for free vertical movement in the table body 10 between two pairs of grooved rollers 21, the two pairs being spaced vertically from one another, and the two rollers of each pair engaging opposite sides of the main leg member. The rollers 21 are mounted in two spaced parallel channel members 22, disposed with their mouths facing one another, the members 22 in turn being securely mounted in any suitable manner on the frame 23 of the table body. In this particular embodiment the frame 23 comprises rigid members connected in a box-like structure, to which decorative panels such as 24 are fastened, but other arrangements may be employed, as will be apparent to those skilled in the art. A chain 25 has one end fastened to the lower end of one main leg member (eg the left band member in FIGURE 1) passes vertically upward and over a sprocket 26 at the upper part of the frame, then horizontally and over another sprocket 27; the chain continues vertically downward, passes in a tight loop around a pin 28 mounted on an arm 29 close to one end thereof, and then passes vertically upward and over another sprocket 30, its other end being fastened to the lower end of the other leg member. The arm 2? is pivotally mounted at one end inthe table frame 23 by a horizontal pivot pin 31 for movement in the directions of the arrows 32, the arm extending transversely between the two leg members. The length of the arm is of course determined primarily by the maximum movement required at its free end to accommodate the maximum vertical movement of the leg assemblies 13. A carriage member 33, constituted by a short channel piece with its mouth opening downwards, embraces the arm and is mounted on the arm upper surface for movement longitudinally thereof by means of two spaced rollers 34, which are interposed between the arm upper surface and the base of the carriage channel. The carriage is constrained to move along the arm in the directions of the arrows 35, and over a predetermined range of movement, by a constraining arm 36 of predetermined length. The arm 36 is connected at its ends to predetermined points on the frame 23 and carriage member 33 by respective pivot pins 3 and 38v Means for urging the free end of the arm 29 downwards about the pivot 31, and thereby counterbalancing the weights of the table 12 and the leg assemblies 13, comprise a plurality of tension springs 39 (only four shown), each connected at one end to the carriage 33 and at the other end to another channel member 40, which is disposed with its mouth opening upwards. The channel member 40 is held securely against the urge of the springs by a screw-threaded bolt 41 passing freely through an aperture in a circular cross-section rod 42, the rod being engaged between bracket members 43 on the lower part of the table frame. The bolt also passes through the base of the channel member 40 and through a nut 41' that is held against rotation by its engagement with the side walls of the channel. As the carriage 33 moves along the arm 29 the bolt 41 can rotate about the pivot provided by the rod 42, so that the channels 33 and 40 always face one another and the springs 39 are of minimum length. The tension of the springs 41 is readily adjusted by rotating the bolt 41, the head of the bolt being accessible at all times without removing any part of the table casing. Referring especially to FIGURE 3, it will be seen that the loop of chain 25 about the pin 28 is held fixed by a bolt and nut fastening 44, which passes through opposed links of the chain and is also readily adjusted.

The means by which the table top 12 is retained at any inclination and/ or height to which it has been set by an operator, under control or" a foot pedal 45, are not described herein, since they form no part of the present invention, and for a full description of such means reference is made to my copending application No. 542,162 filed on April 12, 1966.

For convenience in description it will be assumed that the table top is in its uppermost position so that the arm 29 is in its lowest position, with the carriage 33 therefore at its extreme right hand end position (as seen in FIGURE 1), and the springs 39 at their minimum extension. At this point the springs 39 are exerting minimum counterbalance force, but the radial distance of the carriage from the pivot 31 is at its maximum, and the torque applied to the arm 29 about the pivot is proportional to the product of the spring effort and the said radial distance. The operator depresses the foot pedal 45, whereupon the table is released and can easily be moved up and down, since most of its weight is supported by the counterbalance. As the leg assemblies move down the arm 29 rotates upwards and the springs 39 extend, increasing the force with which they urge the arm for downward movement; as the arm moves upwards the constraining arm 36 moves the carriage 33 to the left as seen in FIGURE 1, reducing its radial distance from the pivot 31 and reducing the moment of the force which it applies to the lever arm 29, and thereby compensating for the increase in the spring force; the characteristics of the springs 39, the length of the arm 36, the location of the pivots 31, 36 and 37 are so arranged that the counterbalancing torque provided by the arm 29 is sufficiently constant over the full range of movement of the table and the arm.

Although the invention has-been particularly described as applied to a constant torque counterbalance for a drafting table it can also be applied to other mechanical systems in which an approximately constant torque characteristic is required.

What I claim is:

v 1. A drafting table including a mechanical counterbalance system and comprising a frame, a drafting table leg assembly mounted by said frame for generally vertical movement with respect thereto, a table top mounted by said leg assembly for vertical movement relative to said 4 frame, an arm mounted on the frame formovement about a pivot, means urging the said arm for movement about the pivot over a predetermined range of such movement with a compensated torque characteristic, said urging means comprising a carriage mounted on the arm for radial movement towards and away from the pivot, biasing means connected between the frame and the carriage and urging the carriage and thereby the arm for said movement with a force that changes with the movement, and constraining means operatively connected between the frame and the carriage and constraining the carriage for the said radial movement upon said movement of the arm, such that the change of the radial distance of the carriage from the pivot compensates for the said change of the force provided by the biasing means, andmeans mechanically connecting said arm and said leg assembly whereby the weight of the leg assembly and the table top are counterbalanced by the compensated torque of the arm.

2. A drafting table as claimed in claim 1, wherein the said constraining means comprises a constraining arm of predetermined length pivotally connected to the said carriage and to the said frame, the pivot of the constraining arm being spaced from the pivot of the first-mentioned arm.

3. A drafting table as claimed in claim 1, wherein the said carriage comprises a channel member embracing the arm, and bearing means interposed between the arm and the base of the channel.

4. A drafting table as claimed in claim 2 wherein the said carriage comprises a channel member embracing the arm, and bearing means interposedbetween the arm and the base of the channel.

of the arm, and screw-threadedly connected to the channel Y member to change the tension of the said springs upon rotation of the rod about its longitudinal axis.

References Cited UNITED STATES PATENTS- 1,859,456 5/ 1962 Nestler 1082 2,560,928 7/ 1951 Bockius 108-36 2,710,780 6/1955 Lawes 1082 2,982,050 5/1961 May 1082 3,123,024 3/1964 Bronson 108136 3,140,559 7/1964 Grow et al 108-10 XR 3,213,809 10/1965 Kritske 108-146 3,273,517 9/1966 Amthor et al 1082 BOBBY R. GAY, Primary Examiner.

GLENN O. FINCH, Assistant Examiner. 

